We plan to investigate the functional relations between primate motor cortex cells and specific arm muscles by recording their acitivty in mokeys trained to perform appropriate responses. During alternating wrist movements against servocontrolled loads corticomotoneuronal (CM) cells will be identified by characteristic post-spike facilitation of muscle activity in spike-triggered averages (STA). We will then crosscorrelate the activity of CM cells with individual motor units in the faciliated muscles and quantitatively compare their activity during graded force responses. Under isometric conditions we will investigate the functional relation of CM cells to specific forearm muscle by operantly conditioning the following response patterns: (a) operant bursts of the CM (b) bidirectional dissociation of the CM cell from its facilitated muscles an (c) coactivation of the CM cell with synergists and antagonists of its facilitated muscles; STA's will be compiled to document patterns of post-spike facilitaton or suppression. Input-output relations of CM cells will be investigated by documenting their sensory responses to natural stimulation and to load perturbation. Interconnections of CM cells with each other and with motoneurons will be further analyzed using single pulse microstimulation near CM cells. In subsequent acute experiments with the same monkeys we will investigate the synaptic connections between CM cells and identified cervical motoneurons by intracellular recording of post-synaptic potentials evoke by cortical microstimulation at CM sites.